O2 sensor damaged?

The pipe between the converter and muffler rotted out. We had it replaced by our mechanic and he reset the CEL. Drove the truck home in the rain, it got very loud about halfway home. We looked at it in the morning after it stopped raining and found our mechanic had forgotten to bolt the O2 sensor back into the pipe he replaced and it was just dangling. Drove back up, he bolted it in, reset the CEL light again. The next day the CEL came back on. I hooked up my OBD2 and it pulls the code 0420. I'm guessing the sensor got damaged when it was hanging down? We had no CEL light prior to the pipe letting go. I'd rather just get a new sensor myself and throw it on than have to take more time off to get this fixed. Worth the money to do that or is it more likely the converter itself?

A new sensor is around $75 (and get a Denso part), a new cat conv is hundreds.